Perishable goods are commonly transported in a controlled environment within an enclosed space such as a cargo box of a truck, trailer, container, or intermodal container. A refrigeration system, also known as a transport refrigeration system, is used in operative association with the enclosed space within the cargo box for controlling the temperature of the air within the enclosed space. The refrigeration system is operative to maintain the air temperature within the enclosed space within a desired temperature range selected for the particular type of perishable goods stowed within the cargo box. The refrigeration system includes a refrigeration unit including a refrigerant compressor and condenser disposed externally of the cargo box and an evaporator disposed within the enclosed space of the cargo box. The compressor, condenser and evaporator are connected in a refrigerant circuit in series refrigerant flow relationship in a refrigeration cycle. When the refrigeration system is operating, air is drawn from within the enclosed space, passed through an evaporator disposed within the enclosed space in heat exchange relationship with the refrigerant circulating through the refrigerant circuit to be cooled, and then supplied back to the enclosed space. Although typically operated in the cooling mode, the refrigerant unit may be equipped with means for heating the air passing through the evaporator in the event that the temperature within the enclosed space falls below the lower limit of the desired temperature range.
Certain perishable products, such as fresh fruits, vegetables and flowers, produce carbon dioxide as a product of the respiration process. In a closed environment, as the carbon dioxide concentration rises, the oxygen concentration drops. If the oxygen concentration gets too low or the carbon dioxide concentration gets too high, the produce can spoil. Additionally, certain fruits and vegetables and flowers release ethylene and/or ethylene compounds as a byproduct of the ripening process. The presence of ethylene based gases within the enclosed space of the cargo box is known to promote the ripening process.
To alleviate these conditions, it is known to introduce fresh air into the closed environment within the cargo box, as well as to vent air from the closed environment within the cargo box. For example, U.S. Pat. No. 6,763,677 discloses a manually operated fresh air vent associated with a refrigerated transport container for providing fresh air to the circulating air and exhausting a portion of the circulating air exteriorly of the cargo box of the container. The vent structure includes an assembly of a generally planar cover having a pair of diametrically opposed flow path openings and a planar cover door rotatable with respect to the cover and also having a pair of diametrically opposed flow path openings. When the door is rotated to bring the respective pairs of openings into alignment, two flow paths are opened, one through which fresh air is introduced into the circulating air and the other through which a portion of the circulating air is exhausted.
Another vent structure commonly used in connection with refrigeration systems commercially available from Carrier Corporation consists of a generally rectangular cover plate having a single opening therethrough that is disposed over and translatable with respect to a panel having a pair of spaced flow path openings. When the opening in the cover plate is positioned between the spaced openings in the panel therebeneath, both flow paths are closed. The cover plate is sized such that when the opening in the cover plate is translated into registration with one of the openings in the panel, both flow paths are opened, one through which fresh air is introduced into the circulating air and the other through which a portion of the circulating air is exhausted.
Although both of the aforementioned vent structures have performed well in service, the potential exists for exhausted air passing out of one opening being entrained in the fresh air being admitted through the other opening due to the close proximity of the pair of openings and the parallel alignment of the incoming fresh air flow and the discharging exhaust air flow. Therefore, it would be an improvement to provide an air exchange assembly structure having a reduced potential for entrainment of exhaust air into the incoming fresh air.